In medical fields, radiation emission computed tomography (ECT: Emission Computed Tomography) apparatus is used that detects an annihilation radiation (for example, gamma rays) pair emitted from radiopharmaceutical that is administered to a subject and is localized to a site of interest for obtaining sectional images of the site of interest in the subject showing radiopharmaceutical distributions. Typical ECT equipment includes, for example, a PET (Positron Emission Tomography) device and an SPECT (Single Photon Emission Computed Tomography) device.
A PET device will be described by way of example. The PET device has a detector ring with block radiation detectors arranged in a ring shape. The detector ring is provided for surrounding a subject, and allows detection of radiation that is transmitted through the subject.
Such radiation detector arranged in the detector ring of the PET device is often equipped that allows position discrimination in a depth direction of a scintillator provided in the radiation detector for enhanced resolution. First, description will be given of a configuration of a conventional PET device. As shown in FIG. 10, a conventional PET device 50 includes a gantry 51 with an introducing hole that introduces a subject, a detector ring 53 having block radiation detectors 52 for detecting radiation being arranged inside the gantry 51 as to surround the introducing hole, and a support member 54 provided as to surround the detector ring 53. Each of the radiation detectors 52 has a bleeder unit 55 with a bleeder circuit in a position between the support member 54 and thereof for connecting the support member 54 and the radiation detector 52.
The PET device determines annihilation radiation pairs emitted from radiopharmaceutical. Specifically, an annihilation radiation pair emitted from inside of a subject M is a radiation pair having traveling directions opposite by 180 degrees.
In order to use such PET device 50, variation in sensitivity is firstly obtained that is used for image correction. Specifically, a cylindrical phantom as a generating source of annihilation radiation pairs is inserted into the gantry 51, and the detector ring 53 detects annihilation radiation pairs (see, for example, Patent Documents 1.) Here, although annihilation radiation pairs are uniformly emitted from the entire phantom, the detector ring 53 does not necessarily output a result that annihilation radiation pairs are uniformly emitted from the entire phantom. That is because detection sensitivity of radiation varies in each radiation detecting element that forms the detector ring 53. Accordingly, some image artifact may fall in an image having imaged distribution of annihilation radiation pairs inside the gantry 51, which corresponds to variation in detection sensitivity of annihilation radiation pairs that the detector ring 53 uniquely has.
The image artifact is superimposed also on a radiological image with a subject image falling therein. Image processing that cancels the image artifact is performed to the radiological image, whereby variation in sensitivity falling in the radiological image is cancelled. Accordingly, a clear radiological image with only the subject image falling therein may be obtained. That is, the phantom as a radiation source is inserted in advance to the detector ring 53 prior to performance of tomography of the subject for determination of variation in detection sensitivity.    [Patent Literature 1] Japanese Patent Publication No. H10-2965